Project Summary: Ruptured abdominal aortic aneurysm (AAA) is the 10th leading cause of death in men over age 55 in the US with mortality of ruptured AAA exceeding 80%. Up until recently, to prevent ruptures, elective Open AAA repair was typically performed with mortality of d5%. Within the last decade, endovascular AAA repair was introduced as a less invasive alternative to open repair. FDA approval for stentgraft repair of AAA in the United States was granted in 1999 and the use of endovascular repair has steadily grown since that time, replacing open surgery for many patients. Over 40,000 AAA repairs are performed annually in the United States and by 2005, 56% of all elective AAA repairs performed in the Medicare population were endovascular. Endovascular AAA repair has been shown to have a lower operative mortality and morbidity than open repair in short-term head to head comparisons. However, recent randomized trials have not demonstrated a sustained mortality benefit with endovascular repair. Endovascular repair also requires costly follow-up surveillance and there is a greater need for re-interventions, although endovascular technologies continue to evolve. In order to understand the comparative effectiveness of various interventions, it is important to extend inquiry beyond small randomized controlled trials of ideal populations to study interventions in real world settings using observational data. In the case of AAA repair, access to comprehensive data from the Medicare program represents an ideal setting in which to perform comparative effectiveness studies as the vast majority of AAA repairs (70%) are performed in this elderly population. Medicare data are also ideally suited to studies that include longer term follow-up and the occurrence of uncommon complications. The specific aims of this proposal are: 1) To study the long term outcomes of endovascular versus open AAA repair in a comprehensive sample of Medicare patients undergoing elective repair; 2) To determine whether changes in technology, as measured by the introduction of new endovascular products over time, has impacted both perioperative and long term survival of those undergoing endovascular repair; and 3) To rigorously define, quantify, and measure the impact of laparotomy related complications in the case of open AAA repair and graft-related complications in the case of endovascular repair.